Our problem is the the number of simultaneous connections we can support isn't static, it varies depending on the type of traffic bursts (i.e. New vs. Returning users).
But agree that a higher level proxy is useful - because this way your overloaded application doesn't even need to deal with traffic (we hope to use toobusy to have applications instruct the routing layer to temporarily block / reroute traffic in times of load).
The reason that I asked that is I feel that most applications end up needing something at that layer eventually anyways, but not knowing exactly what level of traffic results in too much load is a good reason to do this.